Multi-part combustible casting pattern having bend-resistant glue-less joints

ABSTRACT

Combustible low density polystyrene casting patterns and their gate portions are securely assemble at mating surfaces, by forcing integral reverse-tapered tongues into tapered undercut grooves. A tool insertion opening into the undercut of each groove permits carving the pattern parts by a powered rotating cutting tool. The tongues and grooves are so proportioned that the partial elasticity of the low density polystyrene offsets permanent deformation suffered on assembly. Their interfit provides a tight joint sealed against the entrance of casting sand and which resists ending when sand is packed about the assembled pattern.

United States Patent Gross 1541 MULTI-PART COMBUSTIBLE 1 CASTING PATTERN HAVING BEND- RESISTANT GLUE-LESS JOINTS [72] Inventor: Jerome A. Gross, Clayton, Mo.

[73] Assignee: John T. Parsons, Traverse City,

Mich.

[22] Filed: May 4, 1970 [21] Appl. No.: 34,418

[52] US. Cl .,.164/246 [51] Int. Cl ..B22c 7/02 [58] Field of Search ..164/34, 45, 235, 242, 246, 164/24, 35, 36; l8/DlG. l2, 12 F; 249/99,

287/2092 J 20.92 K, 20.92 L, 20.92 T;

[56] References Cited UNITED STATES PATENTS 2,830,343 4/l95-8 Shroyer .I...- ...,164/3.4 3,410,474 11/1968 Keil ..46/25 ux 3,252,260 5/1966 Mills ..52/476X 2,714,269 8/1955 Charles ..46/26 51 Oct. 3, 1972 2,691,242 10/ l 954 Young ..46/25 3,442,311 5/ I969 Rhyne ..287/20.92 J 3,554,236 l/l97l Rhodes ..46/25 X FOREIGN PATENTS OR APPLICATIONS 812,671 4/ l 959 Great Britain ..52/5 94 Primary Examiner j. Spencer Overholser Assistant Examiner-John S. Brown ABSTRACT Combustible low density polystyrene casting patterns and their gate portions are securely assemble at mating surfaces, by forcing integral reverse-tapered tongues into tapered undercut grooves. A tool insertion opening into the undercut of each groove permits carving the pattern parts by a powered rotating cutting tool. The tongues and grooves are so proportioned that the partial elasticity of the low density polystyrene offsets permanent deformation suffered on assembly. Their interfit provides a tight joint sealed against the entrance of casting sand and which resists ending when sand is' packed about the assembled pattern.

4 Claims, 4 Drawing Figures PATENTEDuma 1972 saw 2 or 2 /N\/E/\/TOF? JEROME A. 2055 ATTORNEY 1 MULTI-PART COMBUS'ITIBLE CASTING PATTERN HAVING BEND-RESISTANT GLUE-LESS JOIN'IS BACKGROUND OF INVENTION This invention relates to the making of combustible patterns for castings, using materials such as expanded polystyrene; and particularly, to effecting secure, bendresistant alignment of patterns assembled of several parts, including a gating part. Such. .COmbustible patterns are used for cavity-less casting. After sand is packed around them,the charge of molten metal burns away or vaporizes the casing parts.

r In constructing such patterns, the practice heretofore has been to cut pieces of boards of low density polystyrene and glue them together, much in the same manner as wooden patterns have heretofore been constructed. However, insufficient adhesion is a constant danger. Furthermore, the adhesives utilized are not combustible at as low a temperature as the expanded polystyrene material, and unless the amount of adhesive material is minimized, it may form inclusions in the castings, to render them worthless.

It has. recently been discovered that complex casting patterns maybe made by carving large billets of expanded polystyrene, using tape controlled milling machines. This process minimizes the number of parts to be joined. As to such parts, however, the problem remains how to maintain alignment while the molding sand is packed.

One of the combustible pattern parts, which must be so maintained in alignment, is the combustible pouring gate riser part. The forces of packing sand about such a riser part, may displace it entirely from the remainder of the pattern. As to other pattern parts, even slight displacements of one from another-may render the casting worthless; for example, if a bore is to be drilled through an outer wall into an interior web.

SUMMARY on THE lNVENTlON A principal purpose of the present invention is to provide multi-part combustiblepattems which are not only self-aligning on assembly, but whose assembly with each other provides strong resistance to bending, so that when sand is packed adjacent to them they will not be inferior to integrally formed patterns. Further purposes are to provide strong bending resistance at the attachment of pouring gate riser parts of such patterns; and to permit easy assembly of carved pattern parts at the foundry when they are to be cast. Another purpose is to so proportion the joints of said parts as to positively exclude molding sand using the partial elasticity of the polystyrene material to overcome the partial permanent deformation attendant to assembly. A still further purpose is to provide detailed joint portions which may be carved by a powered rotating cutting tool. 1

To achieve these purposes, I utilize a plurality of pattern parts, including for example a pouring gate riser part, formed of a low density material combustible under a charge of molten metal to be cast, preferably a self-adhered beads of expanded polystyrene of a density between 1 and 3 pounds per cubic foot. The pattern parts have mating surfaces which are brought into abutment when an integral tongue, which extends from the mating surface of a first part is pressed into an undercut groove formed inthe mating surface of a second part.

Both the tongue and groove are formed with reverse tapers. From a narrowed tip, the tongue widens to a taperingthickness, at a level spaced outwardly from its mating surface, in excess of the width of the tapering groove of the second part at equal spacings inwardly from its mating surface. The amount of such excess at least equals the amount of permanent deformation which results from forcing the tapering width of the tongue through the entrant slot of the groove. The partial elasticity of the expanded polystyrene material restores the tongue thickness sufiiciently to hold its reverse taper securely within the reverse taper of the groove. The interfit of the reverse tapers provides a bend-resistant joint without using any adhesives.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is aperspective view, partly broken away, of two pattern parts formed of combustible pattern material, employing the bend-resistant tongue and groove join of the present invention.

FIG. 2 is an enlarged fragmentary cross-section taken along line 2-2 of FIG. 1.

FIG. 3 is a similar section taken along the line 3-3 of FIG. 1.

FIG. 4 is an exploded perspective view of an alternate embodiment, being the assembly of a combustible pouring gate riser pattern part to a second combustible pattern part.

DESCRIPTION OF THE PREFERRED EMBODIMENT Expanded polystyrene bead of relatively low density, particularly in the range of l to 3 pounds per cubic foot, has the property of being only partially elastic when subjected 'to compression. Published figures relating to the mechanical properties of such material (see Bulletin 9-253 of Sinclair-Koppers Company, dated Jan. 1969) shows that after a deformation in compression of 20 percent of its thickness, material of 1 pound per cubic foot density will have been permanently set by only 5.4 percent; whereas material of 3 pounds per cubic foot density will have suffered 9.8 percent permanent set. Thus, the lighter densities are highly desirable for their relative elastic qualities; but

even at such lighter densities an appreciable permanent set will be encountered. The present invention, of a multi-part casting pattern made of this material without the use of glue and relying on the elasticity of the material, is constructed by machining billets of the materials using tape controlled machines driving rotatable tools, such as milling machines.

In the first embodiment of invention, shown in FIGS. 1, 2 and 3, a multi-part combustible pattern is formed for glueless interlocking, for a generally rectangular casting such as is used for a machine base. It includes an upper pattern part generally designated 10, carved of low density polystyrene material as above set forth to an open-bottomed, somewhat hollow, box-like configuration; and a lower pattern part generally designated 1 l which is open topped, and may be of such size as to have its walls aligned with the upper part 10. The lower pattern part 11 has inner wall surfaces 12 and outer wall surfaces 13, the thickness of the wall between them being somewhat exaggerated in the drawings. Similarly, the upper pattern part 10 has inner wall surfaces and outer wall surfaces 15.

Extending horizontally between the inner and outer wall surfaces l2, 13 of the lower pattern part 11 is a horizontal upwardly presented mating surface 16. A downward presented horizontal mating surface 17 extends between the inner and outer walls 14, 15 of the upper pattern part 12. Midway between these wall surfaces around the entire perimeter of the side walls of the upper mold part 10, a tongue 18, best shown in FIG. 2, projects downwardly. At the mating surface 17, it is of constant thickness around the entire perimeter. Below the surface 17 the tongue 18 has reverse tapering side surfaces 19 which may initially be cut to somewhat rounded configuration as shown, and which taper to a narrow tip 20.

To accommodate the tongue 18, a groove 21 is cut into the mating surface 16 which is the upper rim of the lower pattern part 11. Commencing with an entrant slot portion 22, which is slightly wider than the end of the tongue tip 20, the groove 22 extends downward a short distance, and then spreads out in reverse tapering wall portions 23, downward and inward of the mating surface 16, which form an undercut therebeneath.

The reverse tapering side surfaces 19 of the tongue 7 18 define a tapering tongue portion whose thickness, at spacings outwardly from the mating surface 17, are in excess of the width of the groove 20, as defined by its reverse tapering wall portions 23, at equal spacings inwardly from its mating surface 16. The excess thickness of the tongue 18 is at least equal to the amount of permanent deformation which results to the tongue 18 from being forced through the entrant slot portion 22 of the groove 21. Hence, even through the expanded polystyrene material is only partly elastic, this partial elasticity restores the tongue thickness sufficiently, after the tongue has been forced through the entrant slot 22 and into the groove 21, to hold the tongue and groove 18, 21 securely in a bend-resistant joint. After so being forced into the groove 21, the reverse tapering side surfaces of the tongue 19 will be in the permanently deformed position 25 shown in phantom lines in FIG. 2; and the wall portions 23 will have suffered compressive deformation to spread them to the positions shown by the phantom lines 26.

Providing slight clearance between the bottom 27 of the groove 21 and the tip of the tongue 18, assures that the partial elasticity of the material will urge the mating surfaces 16, 17 into tight abutment, forming thereby a secure bend-resistant dovetailed sealed joint, without the use of any fastening means such as glue.

In order to accommodate a tool having a configuration to form the undercut of groove 21, a tool insertion opening 24 is provided at least at one point in the mating surface 16, substantially midway between the inner and outer surfaces of the wall 12, 13. It may be in an area where the wall of the part 11 is enlarged to greater thickness, as shown in FIGS. 1 and 3. The tool insertion opening 24 extends substantially cylindrically downward as there shown, the diameter of such cylinder being equal to the greatest width of fhe tapering groove 21. This permits the groove 21 to be cut by driving a reverse tapered cutter downward and then causing it to move linearly midway between the inner and outer wall surfaces 13, 12.

Assembly of the parts 10, 11 together is done by merely pressing the upper part 10 downwardly so that the tongue 18 is forced through the entrant slot 22 and enters into the groove 21, compressing it and being compressed by it. The permanent deformation suffered when the parts are forced together is compensated for, while the elasticity of the low density material serves to secure the parts firmly together and the abutment of the mating surfaces 16, 17 makes the joint bend-resistant.

The embodiment shown in FIG. 4 illustrates how the invention may be utilized to secure a pouring gate riser generally designated to a typical polystyrene pattern part generally designated 111, here referred to as the lower pattern part. In FIG. 4 only a fragment of such pattern is shown, being for a table casting. A mating undersurface 116 of the pouring gate riser part 110, presented horizontally downward, is attached to abut sealedly against the upper mating surface 117 of the table pattern 1 1 l.

Projecting downward from the mating surface 116 of the riser part 110 is a tongue 118 whose reverse tapering side surfaces 1 19 are formed similarly to the reverse tapering side surfaces 19 of the multi-part pattern previously described. The tongue 118 terminates downwardly in a narrow tip 120.

Within the horizontal table surface 117 of the lower part 111 is a short groove 121 cut in the same manner as has been heretofore described. It includes a substantially vertical entrant slot portion 121, beneath which reverse tapering wall portions 123 provide the desired undercut for the groove 121. At the center of the groove 121 is a tool insertion opening 124 formed substantially cylindrically to merge with the reverse tapering wall portions 123 at their greatest spacing from each other. Using a reverse tapered rotating cutter and working to both sides of the tool insertion opening 124, the result is to leave semi-circular rounded undercut ends at each end of the groove 121. To completely cover and seal these ends, the tongue 118 has plain square cut ends 129, which will not fill the rounded ends 130 of the groove 121. However, the pouring gate riser part 110 has longitudinally extending portions 131 added to extend the undersurface 116 so as to flank both ends 129 of the tongue 1 18.

The riser part 1 10 may be carved by the same pattern carving machine which forms the lower pattern part 111, but is shipped separately to the foundry. At the foundry the parts are assembled for pressing the tongue 118 into the groove 121 until mating undersurface 116 engages sealedly against the upper surface 117 of the lower pattern part 111. The flanking end portions of the undersurface 116 will then overlay and seal off the semi-circular rounded ends 130 of the groove 121.

Referring back to FIGS. 1-3, the interlocked walls of the pattern parts 10, 11 will be bend-resistant, so that when sand is packed against them they will not spread apart from each other to permit sand to enter the joint. Similarly when the FIG. 4 embodiment is utilized, packing sand forcibly about the sides of the pouring gate riser 110 will not cause it to be dislodged; and the partial elasticity of the polystyrene material will hold the tongue 119 and groove 121 interlocked with the surfaces 116, 117 tightly abutted and sealed against each other, without danger of dislodgment.

It is understood that multi-part polystyrene patterns as here described may be treated in conventional ways prior to casting, for example by spray coating with a liquid containing a ceramic, which on drying leaves the joined parts smoothly coated. Since such ceramic coating will not burn as the molten metal is poured, the close bend-resistant interfit of the pattern parts at their tongue and groove joints dispenses with wax fillets which might otherwise be necessary.

I claim: 1. A multi-part combustible pattern for foundry use, comprising a plurality of pattern parts formed of material which is combustible under a charge of molten metal to be cast and which in compression is partly elastic, said plurality of parts having abutting mating surfaces and being formed to shapes which, when assembled at such mating surfaces, make up a desired pattern form, characterized in that a first of said parts has in its mating surface a groove whose cross-section is generally of reverse taper, said groove including a partially cylindrical portion formed on an axis perpendicular to the mating surface of said part, and whose diameter equals the maximum width of said reverse taper cross-section of the groove, further characterized in that a second of said parts has, projecting from its said mating surface, a reverse taper tongue compressively insertable within the reversed taper of said groove,

the said mating surface of said second part being of sufiicient extent to close off the partially cylindrical groove portion by sealed abutment against the said mating surface of said first part,

whereby on such assembly of the pattern, said tongue-and-groove provisions present no surface irregularity.

2. A multi-part combustible pattern as defined in claim 1, wherein the second part is a pouring gate riser part, and

the tongue of said second part projects from and is flanked at its ends by portions of the mating surface of said second part, and the groove of said first part has rounded ends flanked by portions of the mating surface of the first part,

whereby, on assembly, the abutment of the said mating surface portions seals the rounded ends of the groove.

3. A multi-part combustible pattern asdefined in claim 1, wherein the combustible material from which the parts are formed consists of self-adhered beads of expanded polystyrene.

4. A multi-part combustible pattern as defined in claim 3, wherein the polystyrene material has a density in the range of 1 to 3 pounds per cubic foot. 

1. A multi-part combustible pattern for foundry use, comprising a plurality of pattern parts formed of material which is combustible under a charge of molten metal to be cast and which in compression is partly elastic, said plurality of parts having abutting mating surfaces and being formed to shapes which, when assembled at such mating surfaces, make up a desired pattern form, characterized in that a first of said parts has in its mating surface a groove whose cross-section is generally of reverse taper, said groove including a partially cylindrical portion formed on an axis perpendicular to the mating surface of said part, and whose diameter equals the maximum width of said reverse taper cross-section of the groove, further characterized in that a second of said parts has, projecting from its said mating surface, a reverse taper tongue compressively insertable within the reversed taper of said groove, the said mating surFace of said second part being of sufficient extent to close off the partially cylindrical groove portion by sealed abutment against the said mating surface of said first part, whereby on such assembly of the pattern, said tongue-and-groove provisions present no surface irregularity.
 2. A multi-part combustible pattern as defined in claim 1, wherein the second part is a pouring gate riser part, and the tongue of said second part projects from and is flanked at its ends by portions of the mating surface of said second part, and the groove of said first part has rounded ends flanked by portions of the mating surface of the first part, whereby, on assembly, the abutment of the said mating surface portions seals the rounded ends of the groove.
 3. A multi-part combustible pattern as defined in claim 1, wherein the combustible material from which the parts are formed consists of self-adhered beads of expanded polystyrene.
 4. A multi-part combustible pattern as defined in claim 3, wherein the polystyrene material has a density in the range of 1 to 3 pounds per cubic foot. 